std::unary_function is a base class for creating function objects with one argument.

std::unary_function does not defineoperator(); it is expected that derived classes will define this.std::unary_function provides only two types -argument_type andresult_type - defined by the template parameters.

Some standard library function object adaptors, such asstd::not1, require the function objects they adapt to have certain types defined;std::not1 requires the function object being adapted to have a type namedargument_type. Deriving function objects that take one argument fromstd::unary_function is an easy way to make them compatible with those adaptors.

std::unary_function is deprecated in C++11.

[edit]Member types

[edit]Example

#include <algorithm>#include <functional>#include <iostream>#include <vector> struct less_than_7: std::unary_function<int,bool>{bool operator()(int i)const{return i<7;}}; int main(){std::vector<int> v(10,7);    v[0]= v[1]= v[2]=6; std::cout<<std::count_if(v.begin(), v.end(),std::not1(less_than_7())); // C++11 solution:// Cast to std::function<bool (int)> somehow - even with a lambda// std::cout << std::count_if(v.begin(), v.end(),//     std::not1(std::function<bool (int)>([](int i) { return i < 7; })));}

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[edit]See also

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